This invention relates to a reformer that processes a hydrocarbon fuel to separate and provide hydrogen from the hydrocarbon fuel, and in particular, to a composite membrane for an electrochemical autothermal reformer (EATR).
A "reformer" is a known device for converting hydrocarbon fuels to hydrogen, in which a hydrocarbon fuel is mixed with air and with or without steam to convert the mixture to hydrogen, carbon monoxide, carbon dioxide, water, and impurities. An autothermal reformer uses fuel, air, and steam. Since most known reformers are adversely sensitive to the presence of impurities, impurities such as sulphur are generally removed from the fuel before entering the reformer. An electrochemical autothermal reformer combines the principles of electrochemical hydrogen separation with those of an autothermal reformer. The purpose of the electrochemical autothermal reformer is to effect the removal of hydrogen produced from the reaction zone of the reformer so as to drive the reforming reaction to completion by separating or selectively extracting the hydrogen component from the rest of the product mixture.
For example, the principal reactions in a natural gas or "methane" reformer such as an autothermal reformer are: EQU CH.sub.4 +H.sub.2 O.fwdarw.CO+3H.sub.2 Reforming EQU CO+H.sub.2 O.fwdarw.H.sub.2 +CO.sub.2 Shift EQU CH.sub.4 +2O.sub.2 .fwdarw.CO.sub.2 +2H.sub.2 O Combustion
In an autothermal reformer, the exothermic combustion reaction is used to drive the endothermic reforming reaction. The shift reaction is mildly exothermic. If hydrogen is abstracted or removed from the reaction zone of the autothermal reformer, then by LeChatelier's principle, the reforming and shift reactions are driven to completion. Accordingly, the fuel processing in an EATR is greatly simplified since shift converters and selective oxidizers are not required downstream from the fuel processor.
Marianowski et al. (U.S. Pat. No. 4,810,485) teaches a hydrogen forming process and apparatus wherein one side of a hydrogen ion porous and molecular gas non-porous metallic foil is contacted with mixed gases comprising molecular hydrogen formed by a chemical reaction in a hydrogen production zone. During the reaction, the molecular hydrogen is dissociated and passed as ionic hydrogen to the other side of the metallic foil from which it is withdrawn, thereby removing hydrogen from the hydrogen production zone. The concept of the '485 patent above is restricted to the use of a metal foil as the hydrogen separator. Foil separators have been proven to be difficult to achieve in practice. For example, they do not provide for a reliable structure which can operate for a reasonable time at high efficiencies.